This invention relates to end feeding of webs from cassette packages, and more particularly to a system for accurate and automatic connection of a web from a cassette reel to a take-up mechanism in a transport assembly which is external to the cassette. The inventive system is particularly advantageous when used with non-continuous lengths of sprocketed film mounted about a single reel in a cassette.
Cassette loading systems for feeding continuous webs must include a provision for some means to drive a web feeding mechanism. In some cases, it is not necessary to accurately position the web. In cases where it is necessary to accurately position the web, some means of providing information relating to initial position must be included either as information on the web or from a drive mechanism.
In mechanisms using a web feed, it is desireable that most of the web feed mechanism be located outside of the cassette, in order that a single web feed mechanism may be used for a plurality of cassettes.
Film in a continuous web, when unreeled from a cassette, must be wound onto the take-up reel in order to economize on space. If a specialized connector is used at the beginning of the film, this connector can cause the film to bulge at the place on the take-up reel where the connector rests. For this reason, film systems using connectors have not been popular. On the other hand, a connector establishes a positive positioning device. On systems in which it is established that a connector attachment must first be effected in order to effect transport of the film, it is very difficult to inadvertently position the film at an incorrect initial position. The only remaining sources for positional error would then be programming errors and errors derived from misinformation.
In vehicle mounted moving map displays, it is desired that the vehicle's position and orientation correspond to a set of coordinates shown on the displayed map. When map information is provided in the form of a photographic film strip, the information contained in the film strip does not readily convey positional information. Directional orientation and a "y" position are determined by an orientation of a flying spot scanner's raster with respect to the direction and width, respectively, of the film strip, or in a similar manner by mechanical movements. The "x" position, on the other hand, is determined by the distance to which the film is transported out of the cassette feed reel to the mechanism's take-up reel. Film cassettes containing this type of map information are typically indexed by sprockets along the edges of film strip. For example, in one application, 35 mm film which meets the specifications of American National Standard Motion Picture Film is used. Positioning information is provided by a sprocketed capstan. The capstan's total rotational travel is indicated by an encoder assembly driven by the capstan. It is important that the initial position of the film be accurately established in order that a substantial initial positioning error not be transferred to subsequent film indicia.
While it is important that the map be accurately positioned with respect to the vehicle for the purposes of the external visual reference of the pilot or vehicle operator, overlay information is typically provided on a moving map display in conjunction with the map material. For example, a down-looking radar assembly may provide such overlay information, in which the overlay information is expected to more-or-less coincide with the map information. It is important that other information, such as target designations, also coincide with information provided on the map.
In order to accurately establish the initial "x" position of the film strip, it is necessary to carefully feed film leader from the cassette to film leader attached to the take-up mechanism. If this feeding is accomplished to the accuracy of the nearest sprocket, it is possible to identify the initial position of the film strip. Such a procedure has entailed cumbersome manipulation of film leader and was prone to cause positional inaccuracy as a result of the film being inaccurately positioned with respect to its initial sprocket position. Furthermore, prior art manual attachment of film leader from the cassette to film leader in the take-up assembly requires a great deal of manual manipulation of the film in order to achieve the desired result. In cases where the film is inaccessible or where time between different sorties is critical, such as requirement for manual manipulation of film leaders in a map reading system is not acceptable.
It is desired to provide an arrangement for efficiently and accurately connecting film leaders in a cassette to a film leader attached to a cassette drive mechanism. It is therefore an object to provide a quick connect feature for rapidly loading film cassettes. It is a further object to provide a system in which loaded film cassettes are accurately positioned with respect to their initial film position. It is a further object to provide a system for loading film cassettes in which the film or film leader need not be manipulated in order to load the cassette. It is also an object to provide a film cassette loading system in which a film cassette can be loaded into a receiving drive mechanism in a place in which manuevering or visual inspection of the film would be difficult.